We are back to winter with temperatures well below freezing at night. I have seen daffodils in bloom already and people are asking, “Will my flowers freeze?” The answer is, “It depends.”
Although nature designed bulbs to tolerate cold temperatures, how plants, or flowers in this case, respond to low temperatures depends on how low the temperatures go, the stage of flower and leaf development, soil moisture and plant moisture content. All these factors and more influence cold hardiness. In some cases, some varieties may be more cold-tolerant than others.
Cold temperatures rarely harm the bulbs in the ground before they start growing leaves and flowers. Low temperatures prompt the starches in bulbs to break down into glucose, which then acts as a kind of antifreeze lowering the temperature at which water freezes within the plant cells. In addition, the soil acts as an insulator, particularly in northwestern Nevada, since our soil temperature lows are not usually extreme. Mulch on top of the soil, or a layer of snow also help to keep soil temperatures at a moderate freeze level.
Cold stress damages cell membranes due to acute dehydration. The flowers and leaves of daffodils will tolerate some snow and freezing; we’ve all seen daffs growing through the snow at times. However, wet heavy snow can bend or break soft stems and petals and long-term deep freezes kill cells beyond survivability.
Plants are amazing though. When temperatures are less than optimal, “physiological, biochemical, metabolic and molecular changes occur within plants.” Receptors at the cell membrane send signals to the plant to switch on cold-responsive genes to respond to the stress. Plants can sometimes adjust their cellular enzymes to re-stabilize their systems (2010, Yadav, Cold Stress Tolerance Mechanisms in Plants). Of course, their ability to survive has a limited range. At some point, it’s too cold and the plant succumbs.
While temperatures are below freezing at night, you may want to make sure your bulbs are nestled in a bed of mulch to help protect them on the coldest nights. Since it’s hard to cover the flowers with mulch, you could cover them with paper bags (weight the handles of the bags with rocks), buckets, etc. You do have to take the covers off during the day, unless it’s storming. I have been known to go out and gently lift the snow off my daffodils.
I don’t know the low temperature tolerance of daffodils, so perhaps err on the side of caution.
JoAnne Skelly is Associate Professor & Extension Educator, Emerita at University of Nevada Cooperative Extension. She can be reached at email@example.com.